Co XMCD arising from the directional spin alignment.
L
2L
3Technique: X-ray magnetic circular dichroism
J. Heidler,1 C. Piamonteze1 R. Chopdekar,1,2,3 J. Dreiser, C. Jenkins, E. Arenholz, Stefano Rusponi, Harald Brune, L.J. Heyderman, and F. Nolting,1 4 4 5 5 2 1
1 2 3
4 5
,
Swiss Light Source, Paul Scherrer Institut, 5232 Villigen, Switzerland; Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, 5232 Villigen, Switzerland; Department of Chemical Engineering and Materials Science, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA; Advanced Light Source, Lawrence Berkeley National
Laboratory, Berkeley CA 94720, USA; École Polytechnique Fédérale de Lausanne, Institute of Condensed Matter Physics, 1015 Lausanne, Switzerland;
Magnetoelectric coupling mechanisms in the multiferroic composite Co/PMN-PT(011)
[1] Y. Wang et al., (2), 61 .
[2]
[3]
NPG Asia Mater. 2 (2010) D. Pantel et al., Nature materials Vol 11, 289 (2012).
C. G. Duan et al. , PRL 97, 047201 (2006).
Pantel et al.: Ability to control the amount and sign of the interface spin polarization in MTJ’s, [2].
The origin of theTMR sign change is yet under debate and could be assigned to hybridization or charge screening as relevant coupling mechanisms.
Introduction - multiferroic composites and their spintronics potential
Charge driven magnetoelectric coupling Strain mediated magnetoelectric coupling
Dependence on the substrate polarity
- a search using X-ray magnetic circular dichroism
-0.4 -0.2 0 0.2 0.4
0.8 1 1.2 1.4
Electric Field (MV/m) Spinmoment(/atom)mB
H = 0T
XMCD sum rule analysis
strain
interface polarization
This slope dependence (see left figure) is not found in the spin moment obtained from sum rules analysis [8].
Here, it is only relevant, whether the polarization is pointing towards the interface or away from it.
For perpendicular to the plane poled PMN-PT the strain curve inhibits a slope depending on the applied voltage.
References Co on [Pb(Mg Nb )O ] -[PbTiO ] (011)
- a multiferroic composite
1/3 2/3 3 0.68 3 0.32Au (30nm) back electrode
PMNPT (0.5mm) Co wedge (0-7nm)
[01 ]1 [100]
30° grazing X-rays
capping layer Au (2nm)
[ 11]1 [111]
[1 1 1] [11 1] [011]
[100]
[01 ]1
P P
[011]
[11 ]1 [ 1 ]1 1
[1 11] [1 1]1
[100]
[01 ]1
Possible polarization states:Rhombohedral crystal structure [7], 60 C/cmm 2
Relaxor ferroelectric close to the morphotrophic phase boundary
ref.[7] measurement
geometry
Co thickness 3.8nm
magnetic field (T) 0 MV/m after + poling -0.14 MV/m after - poling
Co thickness 5.6 nm
magnetic anisotropy influenced by the spin accumulation /depletion (same in plane strain )!
The thickness is larger then probing depth (TEY). A t is an interface effect.
s expected i
Summary: We observe 2 different coupling mechanisms
Proposed
between a ferromagnet and a ferroelectric coupling mechanisms
hange in interface bonding upon reversing the polariza- tion e.g. Fe/BaTiO [3],[4] .3
Hybridization C
NNNsss
NNNsssNNNsss NNNsss
ME coupling magneto- strictive inverse
piezoelectric
{
Strain
Elastic coupling at the ferromagnet-ferroelectric interface.
energy (eV)0
-4 4
DOS(states/atom/eV)
0 2
2 0 -2
-2
Ti 3d
Fe 3d top interface bottom
Orbital-resolved DOS for interfacial atoms in a Fe/BaTiO3 multilayer [3]
Artificial Multiferroics,
are a route to obtain strong magnetoelectric (ME) coupling at room temperature.
such as ferromagnetic–ferroelectric hetero- structures,
The interactions between the magnetic and electric orders are not only of scientific but also of technological interest, as they could allow the electric control of magnetic properties and lead to new device con- cepts, e.g. multiferroic tunnel junctions (MTJ) [1].
des in contact with insulators, regardless of the details of bonding [5],[6].
Charge screening
Carrier mediated accumulation of spin-polarized carriers is a general characteristic of all ferro- magnetic electro
Co hysteresis curves measured by XMCD along the (01-1) crystal direction for different applied voltages
Co: Thickness 3.8 nm, Total electron yield (TEY) FE FM
FM
-- --
--
- +
+ + ++ +
E-field inducedspin density(Ccm)-3
+30 0 30
FM Dielectric FM
E-field
TMR sign reversal DTER Co/PZT(3.2nm)/LSMO:
resistance(kOhm)
magnetic field (mT)
0 20 40
-40 -20
64 62
5.6 5.5
[4] S. Valencia et al. , Nature materials Vol 10, 753 (2011).
[5] M. Ye. Zhuravlev et al. PRB 81, 104419 (2010).
[6] J. M. Rondinelli et al., Nature nanotechnology Vol 3, 46 (2008).
[7] T. Wu et al., J. Appl. Phys. 109, 124101 (2011).
[8] J. Stöhr, JMMM 200, 470 (1999).
Charge screening
Co spin moment depends on the out of plane polarization direction
Where? interface
[011]
[11 ]1 [ 1 ]1 1
[1 11] [1 1]1 [100]
[01 ]1
Strain
Development of an easy axis (in plane vs out of plane
polarization) Where? bulk
[ 11]1 [111]
[1 1 1] [11 1] [011]
[100]
[01 ]1 P P
inplanestrain(ppm)
Electric Field (MV/m) 0.0
-0.14 0.14
-0.30
-800
-1600 -600
-1000
-1200
-1400
magnetic field (T) magnetic field (T)
magnetic field (T)
magnetic field (T)
normalizedLLXMCD32normalizedLLXMCD32 normalizedLLXMCD32 normalizedLLXMCD32
1.
2.
3.
4.
- poled + poled in plane poled
compare to 5.6nm
thick Co Co thickness 5.6nm
ref.[7]
-(A-2B)mB*nh
I(L )+I(L )3 2
ms,eff=
Tunnel electroresistance (TER) Tunnel magnetoresistance (TMR)
nhNo of 3d holes
A
B Element selective
etermines the spin orientation Sum rules give
[8]:
Surface sensitive XMCD sign d
quantitative information on spin and or- bital angular momenta
